Despite being a significant human health problem, a majority of KSHV studies have been restricted to the overexpression system of the selected viral genes in the absence of viral complete genome and Infection, leading to limited understanding to in vivo KSHV persistence and pathogenesis that are essential in developing safe and effective anti-viral agents and vaccines against this oncogenic pathogen. Specifically, understanding how KSHV gene products contribute to the establishment of persistent infection and pathogenesis requires a reverse genetics approach for the viral genetic deficiencies, an in vitro and in vivo assay system for the viral oncogenesis, and an animal model for the in vivo viral persistence under active host immune conditions. Fortunately, our Program Project Grant (PPG) leaders have recently established a new infectious bacterial artificial clone (BACI6) of KSHV genome that significantly improves the efficiency of the genetic manipulation and virus production (Project 1), a novel system to investigate host's control of the KSHV nucleotide metabolism (Project 2), an efficient KSHV infection and transformation system using primary embryonic metanephric mesenchymal stem cells (MSC cells) (Project 3), and a well-controlled in vivo infection system using a humanized mouse model where KSHV establishes persistent infection and is disseminated into the B and monocyte lineages (Core). Thusly, this multi-disciplinary PPG application is directed toward investigating the host's tricks of Immune recognition and attack as well as the KSHV's tactics of immune evasion and pathogenesis by utilizing recently developed infectious KSHV genetic system, in vitro and in vivo transformation assays, and in vivo humanized mouse models. The major goal of this multi-project grant application is to address (1) how hosts have developed effective mechanisms necessary to control KSHV infection and replication, (2) how KSHV has evolved the various mechanisms necessary to thwart and exploit the host defenses, and (3) how KSHV has conferred the infected cells with oncogenic signatures. This application consists of three Projects with multidisciplinary focused schemes. In addition, the Cores provide an efficient genetic manipulation system for KSHV mutagenesis, a state-of-art humanized mouse model for KSHV persistence and a MSC cell/nude mouse system for KSHV oncogenesis and the Administrative Core provides the overall program milestone and data dissemination.